In the semiconductor industry carrier wafers with several hundred microns thickness are used to fix a product wafer by different processes. Fundamentally it is distinguished between the so-called permanent and temporary bonding methods.
In permanent bonding the carrier wafer and the product wafer are bonded to one another with the intention of no longer being separated from one another. Very often in this case the carrier wafers themselves are the product wafers which at this instant still have a corresponding thickness to act as a carrier to be functionally assigned to the product wafers. These permanent bond methods are diverse, very different and material-specific.
Moreover, it is very often necessary to connect the product wafer to a carrier wafer for a certain time interval in order to be able to carry out other process steps. Very often the product wafers in this temporarily bonded state are back-thinned and in this way reach thicknesses of less than 100 μm, generally less than 50 μm, at present around 20 μm, in the near future probably still less. The temporary fixing must be simple, fast to perform, cheap, efficient, reversible, and physically and chemically stable. Most often the carrier wafers are coated with a bonding adhesive and bonded in a bond method to the product wafer. The temporary bond which has been produced in this way is supposed to withstand high temperatures and forces. The bond interface is supposed to prevent the penetration of liquids and/or gases into the intermediate space of the carrier wafer and product wafer.
The most frequently used type of temporary bonding uses a bond adhesive layer. The adhesive layer can be applied over the entire area of the carrier wafer and/or of the product wafer. This layer has adhesive properties (undetachable interconnection) which are sufficient up to a certain temperature range to adequately fix the two substrates. For separation, the two substrates are heated above this temperature range and thus the cement loses the adhesive properties and these two wafers, the carrier wafer and the product wafer, are separated by application of a horizontal and a vertical force.
The adhesive layer can also be applied only on the edge of the product wafer and/or of the carrier wafer. The inner region does not necessarily contain an adhesive layer. The layer of the inner region can have any properties, but mostly is introduced as support means into the intermediate spaces of the individual bumps. The separation process is similar to the separation process of a blanket bond, in any case only the edge zones need be physically and chemically treated accordingly so that the temporary bond loses its adhesion. This is accompanied by lower temperatures, shorter process times and less material consumption of chemicals.
There are uncounted other methods for breaking a temporary bond again, for example by special lasers and by carrier wafers with small diameter holes through which a corresponding solvent is introduced into the bond over the entire surface.